Fix incorrect unsupported error on synthetic extension call on LHS of ::

#KT-13271 Fixed

compiler/testData/diagnostics/tests/callableReference/bound/syntheticExtensionOnLHS.kt

@@ -0,0 +1,13 @@
+// FILE: A.java
+
+class A {
+    public CharSequence getFoo() { return null; }
+}
+
+// FILE: test.kt
+
+fun test() {
+    with (A()) {
+        foo::toString
+    }
+}